JP7174663B2 - ion detector - Google Patents

Description

The present invention relates to ion detectors.

Configurations of ion detectors applicable to mass spectrometry and the like include, for example, a configuration to which an electron multiplier is applied, a configuration to which a microchannel plate (hereinafter referred to as "MCP") is applied, an MCP and an electron impact diode such as an avalanche diode (hereinafter referred to as "AD"). In particular, a configuration in which an MCP and an electron impact diode are combined is characterized by a long device life and a large maximum output current.

For example, Patent Literature 1 discloses an ion detector in which a mesh electrode and a focus electrode are provided between the MCP and AD. Patent Document 2 discloses an ion detector in which a focus electrode is arranged between an MCP and a semiconductor detection element. Further, Patent Document 3 discloses an MCP detection system in which a gate electrode (mesh electrode) is provided between a first MCP and a second MCP that constitute a tandem structure, and the mesh electrode is output from the first MCP. By applying a delayed potential to the electrons, the electron transfer rate to the second MCP is lowered.

JP 2017-16918 A JP-A-7-73847 Japanese translation of PCT publication No. 2004-533611

As a result of examining conventional ion detectors, the inventors discovered the following problems. That is, ion detection using an MCP is, in principle, as shown in FIG. and When ions (charged particles) are incident on the input surface 10a (the effective area of the MCP 10), electrons are emitted from the output surface 10b in response to the incident ions. Electrons in the vicinity of the output surface 10b are accelerated by the electric field between the MCP 10 and the electron detection surface 20, follow the trajectory 30, and reach the electron detection surface 20. FIG. At that time, the energy (substantially the speed) and the incident angle of the electrons reaching the electron detection surface 20 vary greatly.

When limiting the arrival area of these electrons, an electron lens 30 is arranged between the MCP 10 and the electron detection surface 20 as shown in FIG. Electrons emitted from the surface 10b are converged on the electron detection surface 20. FIG. In FIG. 1B, in order to define the effective area of the electron detection surface 20 and to protect the periphery of the electron detection surface, the signal output device 40 has a mask member 41 made of metal or insulating material. may be provided. Generally, in an ion detector having the structure shown in FIG. 1B, the electron transit time spread (hereinafter referred to as "TTS") is about 150 ps (picoseconds). The energy of electrons emitted from the output surface 10b of the MCP 10 is about 0 to 60 eV, and the spread angle at the time of electron output is about ±30°. Variations in the energy of the electron group and the incident angle θ on the electron detection surface 20 largely depend on the behavior of electrons present near the output surface 10b of the MCP 10. FIG. For this reason, in order to guide electron groups having variations in energy and output angle to the electron detection surface 20 having an effective area with a diameter of about φ=1 mm, it is necessary to suppress the diameter φ of the effective area of the MCP 10 to about 25 mm. (the convergence limit of the electron lens 30).

On the other hand, the effective area of MCP required in the field of quadrupole time-of-flight (Q-TOF) mass spectrometry is diameter φ=40 mm or more. In this case, there is a problem that the conventional electron lens structure cannot sufficiently cope with the expansion of the effective area of the MCP for capturing the ions to be detected.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an ion detector having an electron lens structure capable of expanding the effective area of an MCP for capturing ions. and

In order to solve the above-described problems, the ion detector according to this embodiment includes at least an MCP unit, a signal output device, and a reset unit arranged between the MCP unit and the signal output device. The MCP unit is composed of an ion trapping MCP and a first focus electrode functioning as an electron lens. The MCP has a first input surface and a first output surface which are arranged to face each other and intersect a predetermined reference axis, and respond to the incidence of ions (charged particles) on the first input surface. Then, electrons are output from the first output surface. The first focus electrode is arranged on the first output surface side of the MCP and has a shape surrounding the reference axis. A signal output device is positioned opposite the MCP with respect to the first focus electrode and has an electron detection surface positioned to intersect the reference axis. A reset unit arranged between the MCP and the signal output device is composed of a reset element and a second focus electrode functioning as an electron lens. In this manner, the ion detector realizes an electron lens structure in which a reset element is arranged between two adjacent electron lenses.

Specifically, in the reset unit, the reset element has a second input surface and a second output surface that face each other and intersect the reference axis between the MCP unit and the signal output device. Also, the reset element is arranged such that the second input surface faces the MCP unit and the second output surface faces the signal output device. In addition, the reset element functions to reset both the incident angle variation and the velocity variation of the electrons at the second input surface at the second output surface. The second focus electrode is arranged between the reset element and the signal output device and has a shape surrounding the reference axis.

It should be noted that each embodiment according to the present invention can be more fully understood with the following detailed description and accompanying drawings. These examples are provided for illustrative purposes only and should not be construed as limiting the invention.

Further areas of applicability of the present invention will also become apparent from the detailed description provided hereinafter. However, the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only and various modifications and improvements within the scope of the invention may be made therein. It will be apparent to those skilled in the art from the detailed description.

According to the present invention, an electron lens structure is realized in which a reset element for resetting both the angle of incidence and the velocity of electrons is arranged between first and second focus electrodes, each functioning as an individually controllable electron lens. be done. This allows electrons to be focused to a desired minute area even if the effective area of the MCP for trapping ions is enlarged.

It is a figure for demonstrating the subject of the conventional ion detector. It is a figure for demonstrating the principal part containing an electrode structure of the ion detector which concerns on this embodiment. It is a figure which shows an example of the structure applicable to the reset element and signal output device in the ion detector which concerns on this embodiment. FIG. 2 is a cross-sectional view showing an example of a specific basic structure (a main part including an electrode structure) of an ion detector according to this embodiment; FIG. 4 is a diagram showing an example of a structure for defining effective regions of MCP 110 and reset elements (intermediate MCP 210A) in this embodiment. It is a figure which shows an example of the structure for prescribing|regulating the effective area of the electron detection surface of the signal output device in this embodiment. It is a figure which shows the structural example of the ion detector which concerns on 1st Embodiment. 5 is a graph showing the relationship between the input-output voltage (V) and the gain (output current (A)) of the virtual MCP in the first embodiment; 4 is a graph showing DC linearity (relationship between output current (A) and output current ratio (%)) for virtual MCP in the first embodiment. 4 is a graph showing response time characteristics (time (ns) and output voltage ratio (%)) when a single electron is input for MCPs having effective regions with different diameters. It is a figure which shows the structural example of the ion detector which concerns on 2nd Embodiment. It is a figure which shows the structural example of the ion detector which concerns on 3rd Embodiment. It is a figure which shows the structural example of the ion detector which concerns on 4th Embodiment.

[Description of Embodiments of the Present Invention]
First, the contents of the embodiments of the present invention will be individually listed and explained.

(1) The ion detector according to the present embodiment includes, as one aspect thereof, at least an MCP unit, a signal output device, and a reset unit arranged between the MCP unit and the signal output device. The MCP unit is composed of an ion trapping MCP and a first focus electrode functioning as an electron lens. The MCP has a first input surface and a first output surface which are arranged to face each other and intersect a predetermined reference axis, and respond to the incidence of ions (charged particles) on the first input surface. Then, electrons are output from the first output surface. The first focus electrode is arranged on the first output surface side of the MCP and has a shape surrounding the reference axis. A signal output device is positioned opposite the MCP with respect to the first focus electrode and has an electron detection surface positioned to intersect the reference axis. A reset unit arranged between the MCP and the signal output device is composed of a reset element and a second focus electrode functioning as an electron lens. In this manner, the ion detector realizes an electron lens structure in which a reset element is arranged between two adjacent electron lenses. Note that each of the first and second focus electrodes may be composed of a plurality of electrodes arranged in a state of being spaced apart from each other.

Specifically, in the reset unit, the reset element has a second input surface and a second output surface that face each other and intersect the reference axis between the MCP unit and the signal output device. Also, the reset element is arranged such that the second input surface faces the MCP unit and the second output surface faces the signal output device. In addition, the reset element functions to reset both the incident angle variation and the velocity variation of the electrons at the second input surface at the second output surface. The second focus electrode is arranged between the reset element and the signal output device and has a shape surrounding the reference axis.

According to the ion detector according to the present embodiment having the structure as described above, electrons are incident on the second input surface between the first and second focus electrodes, each of which functions as an electron lens that can be individually controlled. An electronic lens structure is realized in which reset elements are arranged to reset both angular and velocity at the second output face. This configuration allows extension of the effective area in the MCP unit beyond the electronic lens capabilities of the first and second focus electrodes respectively.

(2) As an aspect of this embodiment, the reset element may include an intermediate MCP having a second input surface and a second output surface. In this case, the area of the effective area on the second input surface in the intermediate MCP is preferably smaller than the area of the effective area on the first input surface in the MCP. Further, as one aspect of the present embodiment, the reset element includes a second input surface, a second output surface, an electron input opening provided on the second input surface, and an electron output opening provided on the second output surface. A channel electron multiplier (ChannelElectron Multiplier, hereinafter referred to as “CEM”) having

(3) On the other hand, as one aspect of the present embodiment, the signal output device may include an electron impact diode having an electron capture surface that functions as an electron detection surface. Electron impact diodes include ADs (avalanche diodes) and the like. Further, as one aspect of the present embodiment, the signal output device includes a phosphor having a first surface functioning as an electron detection surface and a second surface facing the first surface, and a second focus for the phosphor. and a photodetector positioned opposite the electrode. The photodetector includes an avalanche photodiode (hereinafter referred to as "APD"), a photomultiplier tube, and the like.

(4) As one aspect of the present embodiment, the ion detector includes a first mesh electrode arranged between the MCP and the first focus electrode, and an ion detector arranged between the reset element and the second focus electrode. It preferably further comprises a second mesh electrode. The first mesh electrode functions as an electrode for extracting electrons (having a velocity or energy of approximately 0) present on the first output surface of the MCP toward the first focus electrode. Also, the second mesh electrode functions as an electrode for extracting electrons (velocity, ie, energy is almost 0) present on the second output surface of the reset element to the second focus electrode side.

(5) As one aspect of the present embodiment, the ion detector includes at least the first input surface of the MCP, the first output surface of the MCP, the second input surface of the reset element, and the second output surface of the reset element. It is preferable to further include a voltage supply circuit for setting each potential. The voltage supply circuit includes a power supply section and a constant voltage generation section. The power supply unit has an electromotive force for ensuring a potential difference between a first terminal electrically connected to the first input surface of the MCP and a second terminal electrically connected to the second output surface of the reset element. give rise to The constant voltage generator holds a first target potential for adjusting the potential of the first output surface of the MCP and a second target potential for adjusting the potential of the second input surface of the reset element. The constant voltage generating section includes a first reference node, a first potential fixing element, a second reference node, a second potential fixing element, and a constant voltage supply section. The first reference node is arranged between the first terminal and the second terminal and set to a first target potential. The first potential fixing element eliminates the potential difference between the first output surface of the MCP and the first reference node. The second reference node is arranged between the first reference node and the second terminal and set to a second target potential. The second potential fixing element cancels the potential difference between the second input surface of the reset element and the second reference node. A constant voltage supply causes a voltage drop to ensure a potential difference between at least the second terminal and the second reference node.

(6) As an aspect of this embodiment, the ion detector may further include one or more auxiliary reset units arranged along the reference axis from the reset unit toward the signal output device. Each auxiliary reset unit includes an auxiliary reset element and a third focus electrode, similar to the reset units described above. The auxiliary reset element has a third input surface located on the side where the MCP unit is arranged and a third output surface located on the side where the signal output device is arranged. Also, the auxiliary reset element resets both the variation in the incident angle and the velocity of the electrons on the third input surface on the third output surface. The third focus electrode is arranged on the opposite side of the third input surface with respect to the third output surface and has a shape surrounding the reference axis. Note that the third focus electrode may also be composed of a plurality of electrodes that are spaced apart from each other.

As described above, each aspect listed in this [Description of Embodiments of the Present Invention] column is applicable to each of all the remaining aspects, or to all combinations of these remaining aspects. .

[Details of the embodiment of the present invention]
A specific example of the ion detector according to the present invention will be described in detail below with reference to the accompanying drawings. The present invention is not limited to these examples, but is indicated by the scope of the claims, and is intended to include all modifications within the scope and meaning equivalent to the scope of the claims. there is In the description of the drawings, the same elements are denoted by the same reference numerals, and overlapping descriptions are omitted.

FIG. 2 is a diagram for explaining the main part including the electrode structure of the ion detector according to this embodiment. As shown in FIG. 2, the ion detector 10A according to this embodiment has a plurality of types of units arranged along the reference axis AX. Specifically, the MCP unit 100, the detection unit 400, and the reset unit 200 arranged on the reference axis AX between the MCP unit 100 and the detection unit 400 are arranged. Note that on the reference axis AX between the reset unit 200 and the detection unit 400, there are one or more auxiliary reset units 300 (part of a group of auxiliary reset units) each having the same structure as the reset unit 200. may be further arranged in series.

Specifically, the MCP unit 100 includes an MCP 110 having a first input surface 110a and a first output surface 110b arranged to face each other and intersect the reference axis AX, and the first output surface 110b of the MCP 110 faces the first input surface 110a and the first output surface 110b. and an electron lens (first focus electrode) 120 arranged at a position where the The reset unit 200 includes a reset element 210 having a second input surface 210a and a second output surface 210b arranged to face each other and intersect the reference axis AX, and the reset element 210 faces the second output surface 210b. and an electron lens (second focus electrode) 220 arranged at a position where the The reset element 210 resets, at the second output surface 210b, both the variation in the velocity (energy) of the electrons at the second input surface 210a and the variation in the angle of incidence of the electrons. The detection unit 400 includes a signal output device 420 having an electron detection surface 400a arranged to intersect the reference axis AX, and a mask member for defining the effective area of the electron detection surface 400a and protecting the periphery of the electron detection surface. 410 (made of metal or insulating material), and

Also, in this embodiment, one or more auxiliary reset units 300 can be arranged between the reset unit 200 and the detection unit 400, each of these auxiliary reset units 300 being similar to the reset unit 200 described above. with the structure of That is, the auxiliary reset unit 300 includes an auxiliary reset element 310 having a third input surface 310a and a third output surface 310b arranged to face each other and intersect the reference axis AX, and a third input surface 310a and a third output surface 310b of the auxiliary reset element 310. and an electron lens (third focus electrode) 320 arranged at a position facing the output surface 310b and having a shape surrounding the reference axis AX. This auxiliary reset element 310 also resets both the variation in the velocity (energy) of electrons on the third input surface 310a and the variation in the angle of incidence of electrons on the third output surface 310b.

FIGS. 3(a) and 3(b) are diagrams (the electron lens is not shown) showing an example of a configuration applicable to the reset element 210 in the ion detector 10A shown in FIG. The example of FIG. 3A is an example in which an intermediate MCP 210A is applied as the reset element 210. FIG. Intermediate MCP 210A comprises a second input surface 210a and a second output surface 210b arranged to face each other. 3B is an example in which CEM 210B is applied as reset element 210. In FIG. The CEM 210B comprises a second input surface 210a and a second output surface 210b arranged to face each other. Second input surface 210a includes electron input aperture 211a of CEM 210B, and second output surface 210b includes electron output aperture 211b of CEM 210B. As shown in FIGS. 3(a) and 3(b), the trajectory 30 of an electron reaching either the second input surface 210a of the intermediate MCP 210A or the electron input aperture 211a of the CEM 210B has its energy (velocity) and the variation in the incident angle is large. Both the intermediate MCP 210A and the CEM 210B, which can be applied as the reset element 210, function to reset both the velocity variation and the angle-of-incidence variation of the electrons at the second input surface 210a at the second output surface 210b.

FIG. 3(c) is a diagram (electron lens not shown) showing an example of a configuration applicable to the signal output device 420 in the ion detector 10A shown in FIG. The example of FIG. 3C is an example in which a phosphor 421 and a photodetector 422 are applied as the signal output device 420 . The phosphor 421 has a second input surface 421a corresponding to the electron detection surface 400a and a fluorescence first output surface 421b that emits fluorescence. As the photodetector 422, for example, an APD, a photomultiplier tube, or the like can be applied.

Note that the following embodiments are limited to the simplest structure in which only the reset unit 200 is arranged between the MCP unit 100 and the detection unit 400. FIG. Specifically, as the reset element 210, the intermediate MCP 210A shown in FIG. It is assumed that AD is applied as the signal output device 420 .

FIG. 4 is a cross-sectional view showing an example of a specific basic structure (main part including an electrode structure) of the ion detector according to this embodiment. FIG. 5(a) is a diagram for explaining the structure for defining the effective area A1 of the MCP 110 in the MCP unit 100 of the ion detector shown in FIG. FIG. 5(b) is a diagram for explaining the structure for defining the effective area A2 of the intermediate MCP 210A in the reset unit 200 of the ion detector shown in FIG. Furthermore, the example of FIG. 6 is a diagram for explaining the structure for defining the effective area A3 of the electron detection surface 400a in AD420A (signal output device 420).

The MCP unit 100 includes an MCP 110 held by an input-side electrode 111 and an output-side electrode 112, a first mesh electrode 130 fixed to the output-side electrode 112 via an insulating spacer, and an electron lens 120. The electron lens 120 is composed of a pair of first focus electrodes 121 and 122 each having a shape surrounding the reference axis AX. One first focus electrode 121 forming part of the electron lens 120 is fixed to the first mesh electrode 130 via an insulating spacer, and the other first focus electrode 122 is fixed to one first mesh electrode 122 via an insulating spacer. It is fixed to the focus electrode 121 . In this MCP unit 100, the TTS of electrons emitted from the MCP 110 is 180 ps. Also, the effective area A1 of the MCP 110 is set to have a diameter of φ=42 mm, for example. Specifically, as shown in FIG. 5(a), the MCP 110 is accommodated within the opening of the insulating spacer 113. As shown in FIG. The input side electrode 111 is in contact with one surface of the insulating spacer 113 . The input electrode 111 is provided with an opening 111a for exposing the central portion of the first input surface 110a of the MCP 110, and the outer peripheral portion of the first input surface 110a is in direct contact with the input electrode 111. On the other hand, the output side electrode 112 is in contact with the other surface of the insulating spacer 113 . The output side electrode 112 also has an opening 112a for exposing the central portion of the first output surface 110b of the MCP 110, and the outer peripheral portion of the first output surface 110b is in direct contact with the output side electrode 112.

The reset unit 200 includes an intermediate MCP 210A held by an input-side electrode and an output-side electrode 212, a second mesh electrode 230 fixed to the output-side electrode 212 via an insulating spacer, and an electron lens 220. The electron lens 220 is composed of a pair of second focus electrodes 221 and 222 each having a shape surrounding the reference axis AX. The other second focus electrode 222 is fixed to one of the second focus electrodes 221 via an insulating spacer. In this reset unit 200, the TTS of electrons emitted from the intermediate MCP 210A is 220 ps. The input-side electrode in the reset unit 200 is the other first focus electrode 122 forming part of the electron lens 120 in the MCP 110, as shown in FIG. 5B. Specifically, the other first focus electrode 122 has a bottom portion 122a that abuts on the intermediate MCP 210A and the insulating spacer 213, and this bottom portion 122a functions as an input side electrode for the intermediate MCP 210A. Further, the bottom portion 122a is provided with an opening 122b for exposing the central portion of the second input surface 210a of the intermediate MCP 210A, and the outer peripheral portion of the second input surface 210a is in direct contact with the bottom portion 122a. The effective area A2 of the intermediate MCP 210A is set to have a diameter of φ=20 mm, for example, by the opening 122b provided in the bottom portion 122a. Intermediate MCP 210 A is housed within an opening in insulating spacer 213 . One surface of the insulating spacer 213 is in contact with the bottom portion 122a of the other first focus electrode 122 functioning as an input side electrode. On the other hand, the output side electrode 212 is in contact with the other surface of the insulating spacer 213 . This output electrode 212 is also provided with an opening 212a for exposing the central portion of the second output surface 210b of the intermediate MCP 210A, and the outer peripheral portion of the second output surface 210b is in direct contact with the output electrode 212. .

The detection unit 400 includes a signal output device 420 having an electron detection surface 400a and a mask member 410 for defining an effective area A3 of the electron detection surface 400a. FIG. 6 shows a specific structure for defining the effective area A3 of the electron detection surface 400a. That is, a mask member 410 made of a metal or an insulating material is placed at the end of the second focus electrode 222, which constitutes a part of the electron lens 220, on the side of the signal output device 420 so as to block the opening of the end. Fixed. The mask member 410 is provided with an opening 411 for defining an effective area A3 (for example, the diameter φ=1 mm) of the electron detection surface 400a. The AD 420A as the signal output device 420 is fixed to an insulating disk 430, and on the outer peripheral portion of one surface of the insulating disk 430, a metal mask member 410 and an insulating disk having a shape surrounding the electron detection surface 400a are provided. An insulating ring 431 is arranged to secure a predetermined space between the electrodes 430 .

(First embodiment)
FIG. 7 is a diagram showing a configuration example of the ion detector 10A according to the first embodiment. An ion detector 10A according to the first embodiment shown in FIG. 7 includes a main part including an electrode structure and a voltage supply circuit. The main part is composed of MCP unit 100 , reset unit 200 and detection unit 400 .

The MCP unit 100 has an MCP 110 having an electron multiplying function, an electron lens 120 , and a first mesh electrode 130 arranged between the MCP 110 and the electron lens 120 . The MCP 110 has a first input surface 110a through which ions (positive ions in the example of FIG. 7) reach, and a first output surface 110b facing the first input surface 110a. Also, in the MCP 110, the resistance value between the first input surface 110a and the first output surface 110b is 10 MΩ. The first mesh electrode 130 is set to the ground potential GND, and functions to extract electrons present near the first output surface 110b of the MCP 110 to the electron lens 120 side. The electron lens 120 is composed of a pair of first focus electrodes 121 and 122 , and one first focus electrode 121 is set to the same potential as the first output surface 110 b of the MCP 110 .

The reset unit 200 has an intermediate MCP 210 A as a reset element 210 , an electron lens 220 , and a second mesh electrode 230 arranged between the intermediate MCP 210 A and the electron lens 220 . The intermediate MCP 210A has a second input surface 210a set to the same potential as the first focus electrode 122, and a second output surface 210b facing the second input surface 210a. Also, in the intermediate MCP 210A, the resistance value between the second input plane 210a and the second output plane 210b is 40 MΩ. In this configuration, the intermediate MCP 210A as the reset element 210 resets both the electron velocity variation and the electron incident angle variation at the second input surface 210a at the second output surface 210b. The second mesh electrode 230 is set at the ground potential GND similarly to the first mesh electrode 130, and functions to extract electrons present near the second output surface 210b of the intermediate MCP 210A to the electron lens 220 side. The electron lens 220 is composed of a pair of second focus electrodes 221 and 222. One of the second focus electrodes 221 is set to the same potential as the second output surface 210b of the intermediate MCP 210A.

The detection unit 400 includes an AD 420A as a signal output device 420 and a mask member 410 for defining an effective area A3 of an electron detection surface 400a of the AD 420A. The AD420A has one terminal connected to the negative potential via the resistor R4 and the other terminal connected to the ground potential GND via the capacitor C. The signal amplified by AD420A is taken out from signal line 600. FIG. The other second focus electrode 222 forming part of the electron lens 220 is connected to a negative potential via a resistor R4, like one terminal of the AD420A.

The voltage supply circuit according to the first embodiment includes at least a power supply section 500 and a constant voltage generation section. The power supply unit 500 includes a first power supply V1 for setting the potential of the first input surface 110a of the MCP 110 via the first terminal T1, and a first terminal T1 electrically connected to the first input surface 110a of the MCP 110. A second power supply V2 for ensuring a predetermined potential difference between the second terminal T2 electrically connected to the second output surface 210b of the intermediate MCP 210A and one of the AD 420A via the third terminal T3 and the resistor R4. and a third power supply V3 connected to the terminal of The first power supply V1 is arranged between the ground potential GND and the first terminal, and generates an electromotive force for setting the potential of the first terminal T1 to -7 kV, for example. The second power supply is a variable power supply arranged between the first terminal T1 and the second terminal T2. An electromotive force is generated so as to secure a potential difference of about 5 kV. The third power supply V3 is arranged between the ground potential GND and the third terminal T3, and generates an electromotive force for setting the potential of the third terminal T3 to -350V, for example.

The constant voltage generator includes resistors R1 to R3 serially arranged between the first terminal T1 and the second terminal T2. That is, the second power supply V2 and the resistors R1 to R3 are arranged in parallel between the first terminal T1 and the second terminal T2. The potentials of the first reference node N1 and the second reference node N2 are set by the resistance ratio of the resistors R1 to R3 arranged in series between the first terminal T1 and the second terminal T2. As an example, the resistor R1 is 3 MΩ, the resistor R2 is 10 MΩ, the resistor R3 is 2.7 MΩ, and the resistor R4 is 1 kΩ. That is, the first reference node N1 located between the resistor R1 and the resistor R2 is electrically connected to both the first output surface 110b of the MCP 110 and one of the first focus electrodes 121. With this line structure, The first reference node N1, the first output surface 110b and one first focus electrode 121 are set to the same potential. A second reference node N2 located between the resistors R2 and R3 is electrically connected to both the other first focus electrode 122 and the second input surface 210a of the intermediate MCP 210A. , the second reference node N2, the other first focus electrode 122, and the second input surface 210a are set to the same potential.

As the operating characteristics of the ion detector 10A according to the first embodiment having the structure described above, the operating characteristics of the virtual MCP composed of the MCP 110 and the intermediate MCP 210A will be described below with reference to FIGS. Also, the convergence limit of a single electron lens will be described with reference to FIG. The first input surface of the virtual MCP corresponds to the first input surface 110a of the MCP 110, and the first output surface of the virtual MCP corresponds to the second output surface 210b of the intermediate MCP 210A. A potential difference (referred to as “input-output voltage”) between the first input plane and the first output plane in the virtual MCP is given by the second power supply V2 of the power supply unit 500. FIG.

FIG. 8 is a graph showing the relationship between the input-output voltage (V) and the gain (output current (A)) of the virtual MCP in the first embodiment (FIG. 7). In this measurement, the potential of one second focus electrode 221, which is set to the same potential as that of the second output surface 210b of the intermediate MCP 210A, is set to -4 kV. The potential of the third terminal T3 is set to -350V by the third power supply V3. As shown in FIG. 8, it can be seen that the linearity of gain and output current is maintained with respect to the input-output voltage of the virtual MCP.

On the other hand, FIG. 9 is a graph showing DC linearity (relationship between output current (A) and output current ratio (%)) with respect to the virtual MCP in the first embodiment (FIG. 7). In this measurement, the potential of one second focus electrode 221, which is set to the same potential as that of the second output surface 210b of the intermediate MCP 210A, is set to -4 kV. The potential of the third terminal T3 is set to -350V by the third power supply V3. The input-to-output voltage of the virtual MCP is set to 3300V. Incidentally, in FIG. 9, as reference data, the measurement results obtained when the input-output voltage of the virtual MCP was set to 2700 V are also plotted. As can be seen from the measurement results in FIG. 9, regardless of fluctuations in the voltage between the input and output of the virtual MCP, the DC linearity deteriorates as the output current increases.

In the ion detector 10A having the structure shown in FIG. 7, a virtual MCP in which two MCPs are arranged in multiple stages via an electron lens has a first input surface (the first input surface 110a of the MCP 110) and a first output surface. (second output surface 210b of intermediate MCP 210A) is fixed in potential. In this configuration, as can be seen from FIG. 8, gain control is possible, but as can be seen from FIG. 9, the DC linearity deteriorates as the gain increases. This is because the resistance values of MCP 110 and intermediate MCP 210A decrease due to heat generation during operation, and the potentials of both first output surface 110b of MCP 110 and second input surface 210a of intermediate MCP 210A decrease due to an increase in output current. This is thought to be due to a decrease (voltage drop). Since the gain increase between the first output plane 110b of the MCP 110 and the second input plane 210a of the intermediate MCP 210A is caused, the linearity (DC linearity) of the virtual MCP by DC voltage control is lost.

In this specification, the term “DC linearity” refers to the ratio of the amount of ions input to the MCP (in terms of current value) to the output current of the MCP (hereinafter referred to as “input/output current ratio”). It refers to the operating characteristics of the MCP. When the amount of ions input to the MCP is small, the input/output current ratio exhibits a constant value (linearity). 10%). This reference value (au) is the input/output current ratio in a range in which DC linearity can be sufficiently secured (a low range of output current of about 1 to 100 nA), and is given by the following equation (1).
Output current (A)/Ion input amount (A) …(1)
On the other hand, DC linearity (%) is given by the following equation (2). Therefore, if the output current is in a relatively low range, the input/output current ratio will inevitably substantially match the reference value (DC linearity is 100%). However, the larger the output current exceeds the above range, the larger the voltage drop on the output terminal side of the MCP, and the greater the difference between the input/output current ratio and the reference value (the DC linearity is lost).
Output current (A) / input amount of ions (A) / reference value (au) x 100 … (2)
Here, the "input amount of ions" is given by the current value resulting from ions reaching the input end of the MCP, and the "output current" is given by the current value resulting from electrons reaching the anode from the MCP.

Next, FIG. 10 is a graph showing response time characteristics (time (ns) and output voltage ratio (%)) when a single electron is input for MCPs having effective regions with different diameters. Note that in FIG. 10, graph G1010 shows the time response characteristics of the first configuration including the MCP, electron lens (focus electrode), and AD having an effective area of diameter φ=25 mm, and graph G1020 shows the time response characteristics of diameter φ=25 mm. Fig. 2 shows the time response characteristics of a second configuration with an MCP, electron lens, and AD with an active area of 42 mm; For the first configuration (graph G1010), the full width at half maximum (FWHW) was 550 ps. In addition, in the case of the second configuration (graph G1020), the FWHW was 570 ps, resulting in deterioration in the time response characteristics compared to the case of the first configuration. From this measurement result, it can be seen that there is a convergence limit with only a single electron lens. Conversely, when electrons are focused on a fixed minute area (for example, an effective area with a diameter of about φ=1 mm), it becomes difficult to expand the effective area of the applied MCP. In this embodiment, a reset unit 200 is provided between the MCP unit 100 and the detection unit 400 in order to solve such problems. The reset unit 200 includes reset elements 210, such as intermediate MCPs 210A, CEMs 210B. This reset element 210 resets both the variation in the velocity of electrons on the second input surface 210a and the variation in the angle of incidence of electrons on the second output surface 210b. By arranging the reset element 210 between the MCP 110 and the signal output device 420, the electron lenses 120 and 220 are provided between the MCP 110 and the reset element 210 and between the reset element 210 and the signal output device 420, respectively. It becomes possible to realize a multi-stage configuration of electron lenses in which are arranged.

(Second embodiment)
As described above, the MCP has a secondary electron emission layer and the like formed on a structure made of lead glass. resistance). In conventional MCPs in which lead glass is applied to the structure, a lead layer deposited by reduction treatment of PbO is used as a resistance layer. In such an MCP, the resistance value of the MCP decreases due to heat generated during operation, and the voltage drop at the output terminal occurs due to the increase in the output current. Since such a decrease in the output potential of the MCP causes an increase in the gain of the MCP, there is a problem that the linearity of the MCP (hereinafter referred to as "DC linearity") by DC voltage control is lost. On the other hand, there are individual differences in resistance values among the manufactured MCPs. Therefore, in fixing the output side potential of the MCP, this "individual difference in resistance between CEMs" must also be taken into consideration.

As means for eliminating the deterioration of DC linearity due to fluctuations in the output side potential of the MCP, for example, a power supply section for setting the input side potential of the MCP and a separate power supply section for setting the output side potential of the MCP. It is also conceivable to prepare a power supply unit for In a configuration in which a plurality of MCPs are arranged in multiple stages via an electron lens, it is necessary to prepare a plurality of power supplies for each MCP. However, such a voltage supply circuit having a plurality of power supply units increases the manufacturing cost of an ion detector in which a plurality of MCPs are arranged in multiple stages via an electron lens, and also reduces the size of the ion detector itself. make it difficult

Therefore, in the second embodiment, by setting a target potential at a reference node that is not affected by fluctuations in the output side potential (and/or input side potential) of the MCP, the target potential can be obtained even at a portion whose potential is not fixed by the power supply section. It has a configuration that allows it to be clamped to a potential. In particular, regarding the fixation of the target potential, there is no need to consider individual differences in resistance values among a plurality of manufactured CEMs.

FIG. 11 is a diagram showing a configuration example of an ion detector 10B according to the second embodiment. An ion detector 10B according to the second embodiment includes a main part including an electrode structure and a voltage supply circuit. Note that the main part in the second embodiment has the same structure as the main part in the first embodiment (FIG. 7). That is, the main part in the second embodiment is composed of the MCP unit 100, the reset unit 200, and the detection unit 400. FIG.

The voltage supply circuit according to the second embodiment includes at least a power supply section 500 and a constant voltage generation section. The power supply unit 500 includes a first power supply V1 for setting the potential of the first input surface 110a of the MCP 110 via the first terminal T1, and a first terminal T1 electrically connected to the first input surface 110a of the MCP 110. A second power supply V2 for ensuring a predetermined potential difference between the second terminal T2 electrically connected to the second output surface 210b of the intermediate MCP 210A and a third terminal T3 to one terminal of the AD 420A. and a connected third power source V3. The first power supply V1 is arranged between the ground potential GND and the first terminal. In the example of FIG. 11, in order to capture positive ions at the first input surface 110a of the MCP 110, an electromotive force is generated to set the potential of the first terminal T1 to -7 kV, for example. The second power supply is a variable power supply arranged between the first terminal T1 and the second terminal T2. An electromotive force is generated so as to secure a potential difference of about 5 kV. The third power supply V3 is arranged between the ground potential GND and the third terminal T3, and generates an electromotive force for setting the potential of the third terminal T3 to -350V, for example.

Constant voltage generator 700A includes resistors R1 to R3 arranged in series between first terminal T1 and second terminal T2, and has a first target potential of first output plane 110b of MCP 110 and a second input plane of intermediate MCP 210A. 210a is held at the second target potential. The first target potential is set at the first reference node N1, which is not affected by potential fluctuations on the first output surface 110b. Also, the second target potential is set at the second reference node N2 which is not affected by the potential fluctuation of the second input surface 210a. Specifically, the potential difference between the second terminal T2 and the first reference node N1 is ensured by the voltage drop across the resistor R2 and the constant voltage supply section 800A (consisting of the resistor R3). The potential difference between the second terminal T2 and the second reference node N2 is ensured by the voltage drop of the constant voltage supply section 800A configured by the resistor R3. A first output surface 110b of the MCP 110, which is set to the same potential as the one first focus electrode 121, and the first reference node N1, is connected by an N-type MOS transistor (hereinafter referred to as "NMOS"). A 1-potential fixing element 710 is arranged. A second potential fixing element 720 made of NMOS is also arranged between the second input surface 210a of the intermediate MCP 210A, which is set to the same potential as the other first focus electrode 122, and the second reference node N2.

A gate G of the first potential fixing device (NMOS) 710 is connected to the first reference node N1. The source S of the first potential fixing element 710 is connected to the first output surface 110 b of the MCP 110 and one first focus electrode 121 . The drain D of the first potential fixing element 710 is connected to the source S of the second potential fixing element 720 . On the other hand, the gate G of the second potential fixed element (NMOS) 720 is connected to the second reference node N2. The source S of the second potential fixing element 720 is connected to the drain D of the first potential fixing element 710, and is connected to the other first focus electrode 122 and the second input surface 210a of the intermediate MCP 210A. A drain D of the second potential fixing element 720 is connected to the second terminal T2.

In this second embodiment, during operation of electron multiplication, as the output current increases (more electrons emitted from MCP 110 toward intermediate MCP 210A), the first output surface 110b of MCP 110 and the second input of intermediate MCP 210A A voltage drop occurs on surface 210a. At this time, both the voltage V _GS between the gate G and the source S of the first potential fixed element (NMOS) 710 and the voltage V _GS between the gate G and the source S of the second potential fixed element (NMOS) 720 increase, When V _GS exceeds the threshold voltage, the first potential fixing element 710 and the second potential fixing element 720 are turned on. When the NMOS is in the ON state, electrons instantaneously flow from the first output surface 110b and the second input surface 210a respectively toward the second terminal T2, resulting in the first output surface 110b of the MCP 110 and the second output surface of the intermediate MCP 210A. The voltage drop on each of the input planes 210a is eliminated. When the voltage drop is eliminated, V _GS also decreases, so that the first potential fixing element 710 and the second potential fixing element 720 are turned off. That is, the potential of the first output plane 110b is fixed to the first target potential of the first reference node N1, while the potential of the second output plane 210b is fixed to the second target potential of the second reference node N2. .

(Third embodiment)
FIG. 12 is a diagram showing a configuration example of an ion detector 10C according to the third embodiment. An ion detector 10C according to the third embodiment includes a main part including an electrode structure and a voltage supply circuit. The main part of the third embodiment has the same structure as those of the first embodiment (FIG. 7) and the second embodiment (FIG. 11). That is, the main part in the third embodiment is composed of the MCP unit 100, the reset unit 200, and the detection unit 400. FIG.

The voltage supply circuit in the third embodiment includes at least a power supply section 500 and a constant voltage generation section 700B. The configuration of the power supply unit 500 is the same as that of the above-described second embodiment (FIG. 11) in which positive ions are captured by the first input surface 110a of the MCP 110. FIG. On the other hand, in the constant voltage generator 700B, a Zener diode TD is arranged between the first reference node N1 and the second reference node N2, and the potential difference between the first reference node N1 and the second reference node N2 is fixed. A constant voltage supply section 800B is composed of this TD and resistor R3. Except for this configuration, the configuration and operation of the constant voltage generation section 700B in the third embodiment are the same as the configuration and operation of the constant voltage generation section 700A in the second embodiment.

(Fourth embodiment)
FIG. 13 is a diagram showing a configuration example of an ion detector 10D according to the fourth embodiment. An ion detector 10D according to the fourth embodiment includes a main part including an electrode structure and a voltage supply circuit. The main part in this fourth embodiment is composed of the MCP unit 100, the reset unit 200, and the detection unit 400. FIG. The MCP unit 100 and reset unit 200 in the fourth embodiment have the same structures as in the first to third embodiments (FIGS. 7, 11 and 12).

A detection unit 400 in the fourth embodiment comprises an AD 420A as a signal output device 420 and a mask member 410 for defining an effective area A3 of an electron detection surface 400a of the AD 420A. The AD 420A has one terminal connected to the other second focus electrode 222 forming part of the electron lens 220 and connected to a node of a predetermined potential via a resistor R4, and a signal output terminal via a capacitor C. with the other terminal connected to the The signal amplified by AD420A is taken out from signal line 600 via capacitor C. FIG. A node located between AD420A and capacitor C is connected to third terminal T3 of power supply section 500A via resistor R6. A Zener diode TD for fixing the potential difference is arranged between the third terminal T3 and the resistor R4.

The voltage supply circuit in the fourth embodiment includes at least a power supply section 500A and a constant voltage generation section. The power supply unit 500A includes a first power supply V1 for setting the potential of the first input surface 110a of the MCP 110 via the first terminal T1, and a first terminal T1 electrically connected to the first input surface 110a of the MCP 110. A second power supply V2 for ensuring a predetermined potential difference between the second terminal T2 electrically connected to the second output surface 210b of the intermediate MCP 210A, and between the second terminal T2 and the third terminal T3 and a third power source V3 for ensuring a predetermined potential difference. The first power supply V1 is arranged between the ground potential GND and the first terminal. In the example of FIG. 13, in order to capture negative ions at the first input surface 110a of the MCP 110, an electromotive force is generated to set the potential of the first terminal T1 to +7 kV, for example. The second power supply is a variable power supply arranged between the first terminal T1 and the second terminal T2. An electromotive force is generated so as to secure a potential difference of about 5 kV. The third power supply V3 is arranged between the second terminal T2 and the third terminal T3, and generates an electromotive force to ensure a potential difference of, for example, 0 to 3.5 kV.

The constant voltage generator includes resistors R1 to R3 serially arranged between the first terminal T1 and the second terminal T2. Also, the constant voltage generator is connected to a circuit within the detection unit 400 via a resistor R5. That is, the resistor R5 has one end connected to the second terminal T2 and the other end electrically connected to the third terminal T3 via the Zener diode TD. A resistor R4 is placed between a node located between the resistor R5 and the Zener diode and one terminal of the AD420A. The potentials of the first reference node N1 and the second reference node N2 are set by the resistance ratio of the resistors R1 to R3 arranged in series between the first terminal T1 and the second terminal T2. As an example, resistor R1 is 3 MΩ, resistor R2 is 10 MΩ, resistor R3 is 2.7 MΩ, resistor R4 is 1 kΩ, and R5 is 20 MΩ. That is, the first reference node N1 located between the resistor R1 and the resistor R2 is electrically connected to both the first output surface 110b of the MCP 110 and one of the first focus electrodes 121. With this line structure, The first reference node N1, the first output surface 110b and one first focus electrode 121 are set to the same potential. A second reference node N2 located between the resistors R2 and R3 is electrically connected to both the other first focus electrode 122 and the second input surface 210a of the intermediate MCP 210A. , the second reference node N2, the other first focus electrode 122, and the second input surface 210a are set to the same potential.

From the above description of the invention, it is evident that many variations of the present invention are possible. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and modifications obvious to any person skilled in the art are intended to be included in the scope of the following claims.

10A to 10D... ion detector, 100... MCP unit, 110... MCP, 110a... first input surface, 110b... first output surface, 121, 122... first focus electrode (electron lens 120), 130... first mesh Electrodes 200 Reset unit 210a Second input surface 210b Second output surface 221, 222 Second focus electrode (electron lens 220) 230 Second mesh electrode 300 Auxiliary reset unit 310a Third input surface 310b Third output surface 320 Electronic lens (third focus electrode) 400 Detection unit 400a Electronic detection surface 420 Signal output device 500, 500A Power supply unit 700A, 700B Constant voltage generator N1 First reference node N2 Second reference node T1 First terminal T2 Second terminal 710 First potential fixed element 720 Second potential fixed element 800A, 800B... Constant voltage supply unit.

Claims (8)

having a first input surface and a first output surface facing each other and intersecting a predetermined reference axis, and receiving electrons from the first output surface in response to incidence of ions on the first input surface; an MCP unit configured by an MCP for output and a first focus electrode disposed on the side facing the first output surface of the MCP and having a shape surrounding the reference axis;
a signal output device having an electron detection surface disposed on the opposite side of the MCP with respect to the first focus electrode and disposed to intersect the reference axis;
a reset unit disposed between the MCP unit and the signal output device;
with
The reset unit
a second input surface and a second output surface intersecting the reference axis while facing each other between the MCP unit and the signal output device, the second input surface facing the MCP unit; and a reset element arranged so that the second output surface faces the signal output device, wherein both the variation in the incident angle and the variation in velocity of the electrons on the second input surface are detected on the second output surface a reset element configured to reset;
a second focus electrode disposed between the reset element and the signal output device and having a shape surrounding the reference axis;
An ion detector comprising: said reset device comprising an intermediate MCP having said second input surface and said second output surface;
2. The ion detector of claim 1, wherein the area of the effective area on the second input surface of the intermediate MCP is smaller than the area of the effective area on the first input surface of the MCP. The reset element is an electron channel having the second input surface, the second output surface, an electron input opening provided on the second input surface, and an electron output opening provided on the second output surface. 2. The ion detector of claim 1, comprising a multiplier. 4. The ion detector according to any one of claims 1 to 3, wherein said signal output device includes an electron impact diode having an electron capturing surface functioning as said electron detecting surface. The signal output device is
a phosphor having a first surface functioning as the electron detection surface and a second surface facing the first surface;
a photodetector disposed on the opposite side of the second focus electrode with respect to the phosphor;
The ion detector according to any one of claims 1 to 3, comprising: a first mesh electrode disposed between the MCP and the first focus electrode;
a second mesh electrode disposed between the reset element and the second focus electrode;
The ion detector according to any one of claims 1 to 5, further comprising: voltages for setting respective potentials of at least the first input surface of the MCP, the first output surface of the MCP, the second input surface of the reset element, and the second output surface of the reset element; further comprising a supply circuit,
The voltage supply circuit is
an electromotive force for ensuring a potential difference between a first terminal electrically connected to the first input surface of the MCP and a second terminal electrically connected to the second output surface of the reset element; a power supply that produces
Constant voltage generation that holds a first target potential for adjusting the potential of the first output surface of the MCP and a second target potential for adjusting the potential of the second input surface of the reset element. Department and
including
The constant voltage generator is
a first reference node arranged between the first terminal and the second terminal and set to the first target potential;
a first potential fixing element that eliminates the potential difference between the first output surface of the MCP and the first reference node;
a second reference node arranged between the first reference node and the second terminal and set to the second target potential;
a second potential fixing element that eliminates the potential difference between the second input surface of the reset element and the second reference node;
a constant voltage supply unit that produces a voltage drop to ensure a potential difference between at least the second terminal and the second reference node;
The ion detector according to any one of claims 1 to 6, comprising: further comprising one or more auxiliary reset units arranged along the reference axis from the reset unit toward the signal output device;
Each of the auxiliary reset units
An auxiliary reset element having a third input surface located on the side on which the MCP unit is arranged and a third output surface located on the side on which the signal output device is arranged, wherein the electron an auxiliary reset element for resetting both the angle of incidence variation and the velocity variation of the third output face;
a third focus electrode disposed on the opposite side of the third input surface with respect to the third output surface and having a shape surrounding the reference axis;
The ion detector according to any one of claims 1 to 7, comprising

Images